Multicellular organisms have evolved elaborate signal transduction pathways for maintaining homeostasis through the control of cell proliferation and death. Programmed cell death or apoptosis is a process in which unwanted cells are eliminated during growth and development (Steller, H. (1998) PNAS 95:5421–5422). Inhibitors of apoptosis proteins (IAPs) constitute a family of highly conserved death-suppressing proteins that were first identified in baculoviruses (Liston, P. et al. (1997) Apoptosis 2(5):423–441). Two homologues have been identified in Drosophila melanogaster (D-IAP and D-IAP-2) and several in rodents and humans including human AAC-11 protein, X-linked inhibitor of apoptosis, XIAP and an XIAP associated protein ZAP-1 (Liston, P. et al. (1997) Apoptosis 2(5):423–441 and Liston, P. et al. (1996) Nature 379:349–352). Several DAD1 (defender against death) proteins have also been identified in mammalian and plant cells (Gallosis, P. et al. (1997) Plant J. 11(6):1325–1331). These proteins appear to be a subunit of oligosaccharyltransferase (OST), an enzyme that is involved in N-linked glycosylation in eukaryotes and may also be associated with programmed cell death in mammalian and plant cells. No genes encoding IAP, IAP-2, ZAP-1 or AAC-11 proteins in plants, especially corn, rice soybean and wheat, have been isolated and sequenced.
There is a great deal of interest in identifying the genes that encode IAPs in plants. These genes may be used to express IAPs in plant cells to enhance cell tissue culture growth. Accordingly, the availability of nucleic acid sequences encoding all or a portion of IAPs would facilitate studies to better understand programmed cell death in plants, provide genetic tools to enhance cell growth in tissue culture, increase the efficiency of gene transfer and help provide more stable transformations.